Phenol dimerizes in benzene. If the observed molecular mass of phenol in solution is 120, its degree — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Theoretical molar mass of phenol ($\text{C}_6\text{H}_5\text{OH}$) is 94 g/mol. Van't Hoff factor $i = M_{\text{theoretical}} / M_{\text{observed}} = 94 / 120 = 0.7833$. For dimerization, $i = 1 - \alpha/2$. Thus, $1 - \alpha/2 = 0.7833 \Rightarrow \alpha/2 = 0.2167 \Rightarrow \alpha = 0.433$. Therefore, correct answer is B.